A conventional bipolar battery generally includes electrodes having a metallic substrate on which positive active material forms one surface and negative active material forms the opposite surface. The active materials are retained by various means on the substrate which is non-conductive to electrolyte ions. The electrodes are arranged in parallel stacked relation to provide a multi-cell battery with electrolyte and separator plates providing an interface between adjacent electrodes. Conventional monopolar electrodes, used at each end of the stack are electrically connected with the output terminals. While achieving respectable power densities, these conventional bipolar battery designs suffer substrate corrosion, seal and active material retention problems. For these reasons bipolar versions of the standard lead acid battery have failed to gain commercial success.
Most bipolar efforts to date have used metallic substrates. Specifically, bipolar lead acid systems have utilized lead and alloys of lead for this purpose. The use of lead alloys, such as antimony, gives strength to the substrate but causes increased corrosion and gassing. In addition to the problems of providing a liquid tight seal between the metallic substrate and adjacent non-conductive case (frame) materials, substrate corrosion, weight and strength factors have also been unacceptable. Furthermore, any attempt to reduce weight has led to increased problems of strength and corrosion. Accordingly a different approach must be used if acceptable weight and life are to be simultaneously achieved. Prior biplate constructions were characterized by the support of active material on the biplate substrate and various physical configurations for purposes of strengthening the biplate such as by providing a supporting grid or frame. Conventional metallic substrates presented seal and corrosion problems.
In the aforesaid copending application Ser. No. 079,476, a light weight bipolar battery construction is disclosed and claimed in which each biplate comprises a composite thermoplastic material with conductive fibers such as carbon graphite or metallic fibers serving as strengthening and conductive elements, each biplate having spaced lead stripes on opposite side surfaces in bonded electrical contact with the graphite fibers. Separator-plates of thermoplastic material are interleaved with the biplates of composite thermoplastic material, each separator-plate having bonded thereto porous resiliently yieldable mats serving to carry and support the active material, to provide transport for gases which form in the battery, and to store electrolyte liquid. Each biplate is bonded to a casing member which in turn is bonded to adjacent casing members. Interleaved biplates and separator-plates are held in a stack under compression by external pressure means and maintained in pressure assembly with active material in contact with the lead stripes. The disclosure of application Ser. No. 079,476 is incorporated herein by reference particularly the concept of providing biplates with lead stripes on opposite surfaces thereof and separator-plates carrying active material interleaved between adjacent biplates and held in pressure assembly by external means.
It should be noted that most prior bipolar battery constructions included biplates having a biplate substrate designed to conduct electrical current therethrough and to assist in the support of active material. The present invention relates to a quasi-bipolar battery construction in which the biplate substrate does not conduct electrical current therethrough. When the term "quasi-bipolar" is used it is meant that the biplate structure does not conduct electrical current through the material of the biplate substrate.